Circuits and systems operating simultaneously can share a reference signal that establishes a common time signal with which operations can be coordinated. One method with which this can be accomplished is with a clock signal that repeats at a given frequency and oscillates between a high and a low state.
Systems connected to the clock signal can synchronize their operations to the clock signal transitions. These synchronized operations can be used in signal processing, data transmission, and/or other types of time-sensitive data operations.
As a clock signal is shared across physical distances, the characteristics of the transmission medium as well as the distance itself can introduce skew into the clock signal as it is perceived by those elements of the system receiving the signal.
For example, clock signals can be implemented across the backplane of a communication system. A “master” clock can generate a master clock signal which is distributed to other elements of the system receiving the clock. These other elements may be timing cards or other types of integrated circuits. Because these signals may experience skew over the transmission distance, the system can provide other time synchronization elements to ensure that the elements receiving the clock signal are correctly synchronized.
One such time synchronization element is a pulse per second (PPS) signal. In traditional systems a PPS signal may have a width of less than one second that repeats once per second. Because the PPS signal specifies a periodic designation of a second and not the actual time, it can be combined with other time source data that provides the full date and time to accurately establish the current time.
One type of signal that can establish the current time is an Inter-Range Instrumentation Group time code (IRIG), such as the IRIG Standard 200-04, a standardized time code developed by the United States Range Commanders Council. The TRIG standard discusses the transmission of time information in a number of different time formats, all with distinct advantages and disadvantages depending on the particular application. IRIG time codes may allow for the transfer of time information between systems by encoding the specific time, including seconds, minutes, hours, days, etc. within the signal through the use of varying the width of pulses defined within specific time frames. IRIG time code is made up of repeating frames, each containing 60 or 100 bits. The bits are numbered from 0 through 59 or 99. The frame time, or the time needed to transfer a time signal, ranges from 10 ms to 1 hour.
Traditionally a clock signal may be transmitted on a backplane of a communication system between cards for synchronization purposes.